The present invention relates generally to silicon nitride film growth, and in particular the present invention relates to the formation of ultra-thin silicon nitride films useful in semiconductor devices such as capacitor structures for integrated circuits.
Remote plasma nitridization (RPN) has been utilized to grow self-limiting ultra-thin nitride films. These ultra-thin films make good dielectric barrier layers in semiconductor devices. For example, dynamic random access memory (DRAM) cells typically comprise a metal-oxide-semiconductor transistor (MOS) and a capacitor used to store signals therein. The capacitors in DRAM cells often utilize an ultra-thin nitride film grown by RPN to act as a dielectric. Higher temperature RPN films are desirable because the films have a slightly higher dielectric constant (k) value that allows the capacitor to store more charges per unit surface area of the capacitor. However, the defectivity in nitride films grown by RPN increases as the temperature during growth increases. Typically, capacitors utilizing nitride films grown by RPN exhibit higher defectivity as evidenced by an increase in capacitor leakage.
Doping and anneals have also been used in semiconductor device manufacturing to condition and dope polysilicon surfaces. For example phosphorous and boron anneals utilizing a rapid thermal process (RTP) may be used to form n-type or p-type lower capacitor electrodes respectively. It is desirable to form silicon nitride films on doped lower electrodes in capacitor structures. However, the doping and the growth of silicon nitride films are generally performed as separate process steps. Thus, there is a need for a process that can integrate doping and nitridization to form ultra-thin nitride films having reduced film defectivity.
This need is met by the present invention that provides methods for forming thin silicon nitride films. These methods may be used in conjunction with conventional processing to provide capacitors having improved cell leakage characteristics.
In accordance with one embodiment, methods of forming a thin dielectric layer for use in a semiconductor device are provided. The methods comprise providing a semiconductor substrate having a surface comprising silicon and forming a silicon nitride layer on the surface. The substrate may be doped with dopant prior to the step of forming the silicon nitride layer, and the dopant may typically comprise arsenic, boron or phosphorous. The doping may be by a rapid thermal anneal (RTA), and the doping may be carried out at temperature of about 700xc2x0 C. to about 800xc2x0 C.
The step of forming the silicon nitride layer may comprise nitridizing the surface of the substrate in a vacuum to form a first growth of silicon nitride and nitridizing the first growth of silicon nitride to form a second growth of silicon nitride. The first growth and the second growth of silicon nitride together comprise the silicon nitride layer. The second growth of silicon nitride is generally self-limiting. The first growth of silicon nitride may be formed in the same process chamber as the doping, and the second growth of silicon nitride may be formed in the same process chamber or a second process chamber. The step of nitridizing the surface of the substrate to form a first growth may be accomplished using a rapid thermal nitridization or a remote plasma nitridization. The remote plasma nitridization may use NH3. The step of nitridizing the second growth may be accomplished using remote plasma nitridization or rapid thermal nitridization, and the remote plasma nitridization may use N2. The forming of the silicon nitride layer may be carried out at a temperature of about 700xc2x0 C. to about 800xc2x0 C. The silicon nitride layer is generally less than about 40 xc3x85 thick, and the layer is more generally about 10-25 xc3x85 thick.
In an alternative embodiment, methods of forming a capacitor are provided. The methods involve forming a lower capacitor electrode, placing the lower capacitor electrode in a vacuum, doping the lower electrode in said vacuum, forming a silicon nitride layer on the surface of the lower electrode, and forming an upper capacitor electrode. The lower electrode may comprise polysilicon or hemispherical grained silicon. The doping of the electrode will generally comprise a rapid thermal anneal. The electrode may be doped with an p-type or n-type dopant. Boron is suitable p-type dopant. Arsenic and phosphorous are suitable n-type dopants. The electrode may be doped at a temperature of about 700xc2x0 C. to 800xc2x0 C.
The step of forming a silicon nitride layer on the surface of the lower electrode generally comprises nitridizing the surface of the substrate in the vacuum to form a first growth of silicon nitride and nitridizing the first growth of silicon nitride to form a second growth of silicon nitride. The first growth and the second growth of silicon nitride together comprise the silicon nitride layer. The second growth of silicon nitride is generally self-limiting. The step of nitridizing the surface of the lower electrode to form a first growth of silicon nitride may be accomplished using a rapid thermal nitridization or a remote plasma nitridization. The remote plasma nitridization may use NH3. The step of nitridizing the first growth may be accomplished using remote plasma nitridization or rapid thermal nitridization, and the remote plasma nitridization may use N2. The first growth of silicon nitride may be formed in the same process chamber used for doping, and the second growth of silicon nitride may be formed in a second process chamber. Alternatively, the doping, first growth, and second growth may be carried out in the same process chamber. The silicon nitride layer may be formed at a temperature of about 700xc2x0 C. to about 800xc2x0 C. The silicon nitride layer is generally less than about 40 xc3x85 thick, and the layer is more generally about 10-25 xc3x85 thick.